This invention relates to methods for agglomerating or binding fine materials or particles to provide agglomerated particles having structural integrity, and to methods for producing agglomerated particulate materials with high liquid absorbencies. "Agglomerating" or "Agglomeration" means consolidating fine materials to form larger intact particles, and thereby substantially changing the size distribution of particles from very fine to coarse. Through the process of agglomeration using agglomerating agents that increase in liquid absorbency of material, the material's utility or desirable qualities are significantly increased.
It would be beneficial if there was some method of agglomerating or binding the fines produced during processing of commodity granule products to provide additional useful product. Particularly helpful would be a method to provide an agglomerated product that has properties similar to the commodity granule products from which the fines were separated.
In the manufacture of granular commodity materials, such as clay animal litter and flour, "dusts" or "fines" are created as an undesired byproduct. These "dusts" or "fines" also include various materials such as metal, metal ore particles and fly ash. When handling such materials in bulk, their dusts can become sources of airborne pollution as well as creating problems in the production of a saleable product. Therefore, these fines create handling problems as well as waste products which cannot be adapted for granular commodity materials. In addition, combustible dusts, such as flour, can be explosive when suspended in a confined air space; and, it may be necessary to continuously filter or scrub the air to prevent combustion.
The grinding of clay ore, to make clay animal litter of a useful particle size distribution, can result in the generation of significant amounts (e.g. 5 wt. percent) of very fine material. The presence of such dust particles annoys consumers, so the dust must be removed in order to make a commercially acceptable product. Typically, the separated clay dust has no commercial value and must be disposed of in a landfill or otherwise.
To be useful as animal litter, particles of agglomerated clay dust would need to have a high degree of liquid absorbency. Other properties, such as wet strength, should equal or exceed those of standard clay litter particles. To date, there has been no successful method of agglomerating clay dust or other particulate materials to form larger particles having a high degree of structural integrity, high wet strength, and an enhanced capacity to absorb liquids.
Ceramics require binders, which are green strength organic materials, to form the ceramic products. These green strength materials aid in process handling, including maintaining the shape or structure of the ceramics before firing.
It would also be useful to have a method for increasing the liquid absorbency of existing particulate materials. Highly liquid absorbent particles are useful in cleaning up spilled liquids such as petroleum products and hazardous substances. The absorbent particles should have the ability to absorb the liquids and still maintain their integrity.
Also, it has been known for many years that cellulose can be synthesized by certain bacteria, particularly those of the genus Acetobacter. But, neither this type of cellulose, nor any other, has been recognized as serving a role in agglomerating fine particles or in increasing the liquid absorbency of existing particulate materials.
It has been known for many years that cellulose can be synthesized by certain bacteria, particularly those of the genus Acetobacter. However, taxonomists have been unable to agree upon a consistent classification of the cellulose producing species of Acetobacter. For example, the cellulose producing microorganisms listed in the 15th Edition of the Catalog of the American Type Culture Collection under accession numbers 10245, 10821 and 23769 are classified both as Acetobacter aceti subsp. xylinum and as Acetobacter pasteurianus. For the purposes of the present invention any species or variety of bacterium within the genus Acetobacter that will produce cellulose under agitated conditions should be regarded as a suitable cellulose producer.
The cellulose fibrils produced by Acetobacter, although chemically resembling, in many aspects, cellulose produced from wood pulp, are different in a number of respects. Chief among the differences is the cross sectional width of these fibrils. The cellulose fibrils produced by Acetobacter are greater than two orders of magnitude narrower than the cellulose fibers typically produced by pulping birch or pine wood. The small cross sectional size of these Acetobacter-produced fibrils, together with the concomitantly greater surface area than conventional wood-pulp cellulose and the inherent hydrophilicity of cellulose, leads to a cellulose product having unusually great capacity for absorbing aqueous solutions.
This capacity for high absorbency has been demonstrated to be useful in the manufacture of dressings which may be used in the treatment of burns or as surgical dressings to prevent exposed organs from surface drying during extended surgical procedures. Such uses and a variety of medicament impregnated pads made by treatment of Acetobacter-produced intact pellicles are disclosed in U.S. Pat. No. 4,788,146.
The pellicles of U.S. Pat. No. 4,788,146 are produced by growing Acetobacter in a culture medium tray which remains motionless. Acetobacter is normally cultured under such static conditions with the cellulose microfibrils being produced at the air medium interface. Most bacteria of this genus are very poor cellulose producers when grown in agitated culture. One reason proposed for such poor production is that an agitated culture induces a tendency for reversion to noncellulose producing strains.
However, certain Acetobacter strains are characterized by an ability to produce large amounts of a reticulated bacterial cellulose in agitated culture without manifesting instability leading to loss of cellulose production in culture. European Patent Application No. 86308092.5 and U.S. Pat. No. 4,863,565 disclose Acetobacter varieties which are vigorous cellulose producers under agitated culture conditions. The reticulated cellulose produced by the disclosed microorganisms and culture conditions appears to be a unique type, physically quite different from other known bacterial cellulose. It has a highly branched, three dimensional, reticulated structure. A normal cellulose pellicle tends to have a lamellar structure with significantly less branching.